DirectMemory容量可通过 -XX:MaxDirectMemorySize指定,如果不指定,则默认与java堆最大值一样,虽然使用DirectByteBuffer分配内存也会抛出内存溢出异常,但它抛出异常时并没有真正向操作系统申请分配内存,而是通过计算得知内存无法分配,于是手动抛出异常,真正申请分配内存的方法是unsafe.allocateMemory()
下面是测试代码:
public class DirectMemoryOOM{
private static final int_1MB = 1024 * 1024;
public static void main(String[] args) throws Exception{
Field unsafeField = Unsafe.class.getDeclaredFields()[0];
unsafeField.setAccessible(true);
Unsafe unsafe = (Unsafe) unsafeField.get(null);
while(true){
unsafe.allocateMemory(_1MB);
}
}
}
执行报错:
Excepiton in thead "main" java.lang.OutOfMemoryError